1. Field of the Invention
The present invention relates generally to a ground fault indicating device. More particularly, a device for indicating locations of ground fault which occur when lightning strikes transmission lines is proposed.
2. Description of the Related Art
Ground fault indicating devices are generally known. A typical indicating device of a related art is disclosed in Japanese Utility Model Examined Publication No. 47-25875. The indicating device disclosed therein has a flash lamp as an indicator. Paint is applied to either an external surface or an internal surface of the flash lamp. The paint is made of a compound which changes its color in accordance with a temperature change. When a current transformer (CT) detects a ground fault current, the current from a secondary current transformer discharges the flash lamp. Thus, the color of the paint is changed by a heat generated by the flashing of the flash lamp, so as to indicate the occurance of a ground fault strike.
In this device, however, the flash lamp is a very small indicator. Therefore, recognizing the location of a ground fault with the flash lamp indicator from a distance is very difficult.
Another type of the indicating device is also disclosed in the above Japanese Utility Model Publication No. 47-25875. In the second device, an indication bar is normally accommodated in a housing. When the current transformer detects a ground fault current, a solenoid coil is energized to protrude the indication bar out of the housing.
In this device, the indication bar is large enough to recognize its protrusion from the distance. However, the required solenoid coil is quite expensive to produce.
In addition to the foregoing devices, another type of the device has been also known. In this device, a secondary current outputted by a current transformer which has detected a ground fault current heats a filament to ignite an explosive. The explosion energy of the explosive protrudes a pipe shape indicator.
However, the housing is exposed to the atmosphere and is liable to deteriorate after an extended use. When the airtightness of the housing deteriorates, the filament and the explosive are exposed to the humidity in the atmosphere. Thus, the ignitability of the filament and of the explosive is significantly lowered, so that the indicator will not function even when lightning strikes and causes a ground fault. Therefore, the housing must be replaced every five years in this type of the device to insure a good airtightness. Accordingly, the costs of using such devices are relatively high due to their short lifespan.